SAUPEC2018: The sky’s the limit for power engineers

The 26th South African Universities Power Engineering Conference (SAUPEC) was hosted by the School of Electrical and Information Engineering of the University of the Witwatersrand, in conjunction with the South African Institute of Electrical Engineers (SAIEE), recently. The event provided a forum for post-graduate students and faculty from the region to present their research work in power-related fields.

In addition to three international key note speakers, 106 papers in four streams, were presented over three days at the conference rooms at the university’s Science Stadium. A number of company presentations were also made during the event.

The conference made it clear that many opportunities exist for engineers in the electrical power field as the world seeks for greater levels of electrification at low cost and with minimal environmental impact.

Key note addresses

Key note speakers including Dr. Rob Stephen, the international president of Cigre and master specialist at Eskom; Jiang Liping, the deputy president of the Chinese State Grid Energy Research Institute, and Prof. Malcolm McCulloch, the head of the electrical power group at the University of Oxford.

Addressing about 165 delegates made up of primarily final-year or postgraduate students, as well as faculty, these three experts discussed the power system of the future, the integration of renewable energy in China’s power system, and a low-cost simple mini-grid system to supply power to rural communities.

The power system of the future – Dr. Rob Stephen, Cigre

Dr. Rob Stephen

Dr. Rob Stephen said that ten factors will affect designs for future power systems:

Distributed generation: The introduction and rapid deployment of renewable energy sources such as wind and solar PV has resulted in electricity being generated at various places on an electrical network. As a result, networks have to manage bidirectional, multi-voltage current flows. This becomes more complex as the grid expands with the advent of intercontinental interconnectors. At the same time, the increase in modern electronics which are powered by DC and the generation of DC by solar PV systems makes the distribution of low-voltage DC more viable, and the need for affordable battery storage essential. The advent of electric vehicles will increase the demand for high-power DC power supplies too.

Digitalisation: Smartgrids, smart meters, modern transducers, the Internet of Things, the control of appliances and equipment remotely, and demand response all rely on modern digital techniques. These digital systems create large amounts of data which has to be managed, stored and processed efficiently. Data overload, which will slow the network down, must be prevented. At the same time, data has to be protected from cyber-attacks.

The emergence of high-power electronic devices: HVDC for transmission networks with low- and intermediate voltage distribution for domestic and small commercial or industrial applications is becoming viable. Hybrid towers carrying both HVDC and HVAC powerlines are being seriously considered as new corridors for additional powerlines are becoming scarce and expensive. Electronic switchers as used in inverter-based systems, especially solar PV systems, introduce harmonics which could interfere with other high-frequency systems.

Energy storage: Behind-the-meter energy storage systems are become more common. These make distribution networks more complex because power cables and switchgear need to be isolated from both the primary energy source (the power utility) and the load (customer) where a customer’s battery could damage equipment or injure technicians working on the distribution network.

New systems: It has been shown that a power system consisting of renewable energy generation only is not feasible, and that a modern power system design will need to consider balancing power from at least four different sources simultaneously. This will require congestion management, active and reactive reserve power, and risk management. Modern technologies allow for far higher voltages than ever before: 1200 kV AC and 1100 kV DC; submarine cables at depths up to 3 km; digital substations with low-cost compact GIS switchgear.

Modern protection concepts: Advanced neural networks with employ artificial intelligence systems allow for relays to be reconfigured “on the fly” according to network requirements. Inverter-based provide no inertia unless accompanied by an energy-storage system. This means that, under fault conditions, line voltage falls too quickly for the network to respond or recover, resulting in a significant and dramatic system failure.

The need for a new approach to system planning: As systems develop and become more sophisticated, and changes in technologies and components are introduced, it becomes difficult to predict how the network will need to be configured. One example of this is with electric vehicles which become mobile loads (as they recharge at various locations) and generators (as they discharge into the network to assist consumers during peak or high-tariff periods).

Advanced tools: Today’s grids, especially the medium- and low-voltage grids, are affected by the vast numbers of inverters and UPSs which are in use. Special tools are needed to measure and analyze waveforms, as well as voltage and frequency responses, to assist in grid modelling and improve the predictability of the grid under different conditions.

Managing assets: Existing assets need to be reconfigured to cope with the new reality. Reverse current flows can cause problems in power transformers where tap-changers cannot cope with differing voltages on the secondary windings.

Stakeholder awareness: In all of this, utilities and customers have to cooperate so that customers fully understand the benefits they gain from new technologies such as smart meters. A proper understanding of electricity markets is essential if a new grid is to be successful.

Power development and the integration of renewable energy in China – Jiang Liping, State Grid Energy Research Institute, China

Jiang Liping

Jiang Liping, describing the Chinese power system, said that seven regional grids provide power to 1,1-billion users living in 88% of the land area.

Total installed capacity is 1777 GW, with an annual energy generation of 6419 TWh. Peak load in 2016 was 939 GW.

China uses both HVDC and HVAC systems: HVDC up to 800 kV, and HVAC up to 1000 kV.

Predictions for the future

The country predicts consumption to grow to between 12 300 and 14 400 TWh in 2050.

Table 1: Planned renewable energy generation over the next 13 years.

Generation technology

2020

2030

Hydro

350 GW

480 GW

Wind

250 GW

500 GW

Solar PV

150 GW

500 GW

Wind and solar

The Chinese government is working on a de-carbonising programme which will see 15% decrease in fossil fuels by 2020, rising to 20% decrease in 2030.

Installed capacity in wind-powered generation grew from 45 to 145 GW between 2011 and 2016, while solar PV grew from virtually nothing, to 75 GW in the same period. In 2017, the installed capacity of wind-powered generation was 164 GW, and solar PV was 130 GW.

Curtailment

Despite the massive growth in renewable energy sources in China, much of it has to be curtailed as a result of a number of challenges the country faces. Wind was curtailed by 17% (49,7 TWh) and PV by 10% (7,04 TWh) in 2016.

Technical constraints

Most of the RE is concentrated in some rural, less populated areas

Limited trans-regional interconnections which cannot carry the additional power

Non-flexible conventional (thermal and nuclear) power generation

Institutional constraints

The lack of ancillary service markets

Inflexible price structures

No demand-side participation by consumers

Future plans

China intends to continue with its de-carbonisation programme and to strengthen its regional interconnections. New lines will be UHV to compensate for voltage drops over very long runs across the country. The country also plans to decouple heat from power generation by encouraging its citizens to use electric boilers for central heating and hot water supply.

Powering Africa from the ground up – Prof. Malcolm McCulloch, University of Oxford

Prof. Malcolm McCulloch

Prof. Malcolm McCulloch, in addressing the challenges of new power grids for Africa, proposed a simple solar PV-plus-battery storage mini-grid solution for rural communities. Siting the statistic that 600-million Africans have no access to electricity, he said that people want services – not electricity. They want to be able to charge and use their mobile phones, to watch TV, have light at night, be able to pump water from a well, etc. These basic services can be provided using a mini-grid concept, Prof. McCulloch said.

He suggested that, in a rural village, a structure should be built upon which PV panels are mounted. This structure becomes a virtual power station feeding the homes in the village with electricity via a simple distribution network. The solution, which he described as being a “hub and home” system, comprises an autonomous hub feeding a few homes with electricity. Each home is equipped with a battery and a DC to DC controller which powers equipment and charges the battery.

Prof. McCulloch said that since more and more appliances operate on low voltage, a 60 V distribution system supplies power to feed low-cost 300 W DC to DC converters which charge batteries and operate appliances in people’s homes. This voltage was chosen because, Prof. McCulloch said, 60 V is “touch safe” yet high enough to allow for the volt-drop caused by the resistance associated with long runs of thin wire which would be used in such an installation.

The system has been tested in Kenya, Prof. McCulloch said, with great success. The cost of a typical installation, including the PC panels, batteries and DC to DC converter, is less than US$ 100 per hub, he said.